RAPID EXTRACTION OF ISOPROTURON AND DIURON FROM GRANULAR ACTIVATED CARBON

This paper describes the development of a rapid extraction method for the recovery of the herbicides isoproturon and diuron from spiked gran ular activated carbon using supercritical carbon dioxide modified with high proportions of various organic solvents. Recovery of the herbici des increased with increasing extraction temperature, decreasing extra ction pressure and increasing proportion of liquid solvent in the CO2 stream, Highest recoveries were achieved when liquid solvent alone was pumped through the extraction cell at high temperature (140 degrees C ) indicating that the liquid solvent facilitates the extraction. Extra ction efficiency of isoproturon and diuron from spiked GAC (0.5 mg g(- 1)) was 75% (rsd 4%) and 41% (rsd 8%) respectively after only 5 minute s extraction with 20 mt dichloromethane:methanol (93:7). Increasing th e extraction time led to the thermal degradation of the herbicides and consequently did not have a perceptible effect on their recovery. Thi s very rapid extraction method has great potential as a screening tech nique for the routine monitoring of organic micro-pollutant concentrat ions in GAC filters. Such information may be used to optimise GAC rege neration time and to reduce the risk of pollutant breakthrough into dr inking water supplies. Copyright (C) 1996 Elsevier Science Ltd